When a pair of bald eagles wove a 5-foot nest of sticks on an isolated hillside in suburban Allegheny County in 2010, it was seen as a sort of environmental milestone -- nature's confirmation that the Pittsburgh region had cleaned up its act.

But the new eagles in town -- two nesting pairs that have taken up residence in sight of high-traffic corridors in Harmar and Hays -- are avian rock stars. Their nesting rituals have been witnessed daily by crowds of fans at viewing sites that have become Allegheny County's newest tourist attractions.

And as local bird-watchers learn the rules of eagle etiquette, Pennsylvania's growing bald eagle population is perhaps within months of being removed from the state's threatened species list.

"Did you ever think you'd live long enough to see three bald eagle nests in Allegheny County?" asked Tom Fazi, southwest region education officer for the state Game Commission.

The pair that nested in Crescent in 2010 failed in their first two breeding attempts, common among eagles. Last year they hatched an eaglet. They've returned to the nest this year, and their offspring has been sighted nearby.

Last year, two bald eagles were spotted numerous times near the Hulton Bridge in Harmar. This year the pair -- a mature female and juvenile male -- have forcibly evicted two red-tailed hawks from their longtime nest site high on the ridge above Route 28 overlooking the Allegheny River. Crowds at a pullover on Freeport Road have witnessed the ongoing interspecies aerial scuffle for control of the nest.

"At first they were just flying around -- you could see the wingspan and white heads. In February, they picked a spot up on the hillside and started building a nest," said Keystone's Michael Thompson. "They don't seem to be bothered by the trains or cars or any of the industry going on down below."

Bald eagles can weigh up to 14 pounds with a wingspan stretching to 7 feet. Females grow larger than the males, and both sexes attain their distinctive white heads and tails at 5 years of age. Thompson said he's seen them soaring over the Glenwood Bridge heading upstream in search of fish.

"It's always interesting when wildlife moves into the neighborhood," he said. "My concern is that someone will disturb them and they won't come back."

Jim Bonner, executive director of the Audubon Society of Western Pennsylvania, said that's possible, especially considering the high-traffic locations where the new eagles have nested. But difficult terrain may keep unwelcome human visitors at bay.

"I stop by the Harmar site almost every day," Bonner said. "There's often a crowd, but so far they've been respectful of the eagles' privacy."

On Sunday, the Audubon Society organized a bald eagle viewing. In about six hours more than 200 people spied them through binoculars and viewing scopes.

"We've had a lot of internal discussions on whether to encourage people to visit (the site)," Bonner said. "We think if there's one easy, safe place where people can get a look, it might keep them from approaching the nest. The more concerned people we have keeping an eye on it, the less chance some yahoo will do something that might scare them."

Fazi said the Game Commission is considering erecting informational plaques on the finer points of eagle etiquette.

"As long as people aren't walking up through the woods near the nests (the birds) should be fine," he said.

Doug Gross, Game Commission nongame and endangered bird supervisor, said giving the eagles 1,000 feet of leeway is a good rule of thumb.

"It's unusual that these new nests are this close to (urban activity), but they wouldn't have nested there if they didn't feel safe," Gross said.

It's not conclusive, but bald eagles are believed to bond for life. Some ritual nesting behavior has been observed at Harmar and Hays, but there's no evidence the new residents are in the family way. In nests that weigh up to 1 ton, eagles lay one to three eggs from February through April. They hatch in the spring. Bald eagles can live up to 30 years.

The federal Bald and Golden Eagle Protection Act of 1940, the ban on the pesticide DDT, and cleaner water have revived the nation's eagle population. More than 220 bald eagle nests are confirmed in Pennsylvania and have produced more than 1,000 eaglets. The bald eagle was removed from the federal list of threatened and endangered species in 2007, but is still listed as a threatened species in Pennsylvania.

"Pennsylvania has a bald eagle management plan (and) parameters for what are considered threatened and endangered species. For about the last three years, bald eagles have met all the criteria for removal from the threatened list," Gross said.

"If all goes well they could be removed from the list by the end of the 2013 nesting season," he said.